An automotive air conditioning system typically includes a condenser mounted in proximity to the front grill, a refrigerant compressor located within the engine compartment, and an evaporator contained in an HVAC housing that is essentially inside the passenger compartment. Internal heat exchangers (IHX), such as the double pipe IHX disclosed in SAE Publication No. 2007-01-1523 and the internal coiled tube IHX disclosed in U.S. patent application Ser. No. 12/487,709 are used to take advantage of the temperature differential between the refrigerant low pressure side and the refrigerant high pressure side to improve the overall cooling capacity of the air conditioning system.
The main inner volume of the compressor, the so called crankcase, is substantially hollow, but numerous moving components are either contained in or exposed to it, such as the central drive shaft and associated support bearings, swash plate, and reciprocating pistons. During operation, the compressor pumps refrigerant through the air conditioning system. The refrigerant carries entrained lubricant oil, also known as refrigerant oil to those of ordinary skill in the art, which reaches and lubricates the various moving part interfaces within the air conditioning system including the moving components within the compressor. When the compressor sits for extended periods of non-operation, it is desirable that a substantial pool of lubricant oil remain at the bottom of the crankcase to be available to lubricate the interfaces during start up.
Observations made prior to the subject invention found that lubricant oil appeared to be actively leaving the compressor crankcase during periods of vehicle and compressor inactivity and settling within the condenser and evaporator, where it would not be immediately available at compressor start up. This phenomenon of lubricant oil migration was found to be caused by a pressure imbalance between the main crankcase volume of the compressor and other components of the air conditioning system. This imbalance was creating a condition by which liquid refrigerant oil, which is miscible in the refrigerant, was subject to a combination of internal siphoning and pushing forces that pushed and pulled the liquid out of the compressor.
U.S. patent application Ser. No. 10/874,046 provides a partial solution to the undesired migration of lubricant oil migration that includes a small pressure equalization passage provided at a high point within the compressor, between the crankcase and suction chamber in the manifold. This reduces the tendency of the liquid refrigerant-oil mixture to be pulled and or pushed out of the crankcase and into the manifold, and ultimately to the condenser. However, this solution does not adequately address the migration of the liquid refrigerant-oil mixture to the evaporator.
It is desirable to have a solution to reduce the tendency of liquid refrigerant-oil mixture migration to both the condenser and evaporator. It is further desirable for a solution that requires minimal modification of existing components of an air conditioning system.